feat(frontend): enforce explicit types and typed HIR codegen

[LunaStev]

Summary

• make LLVM code generation consume TypedProgram semantic facts directly
• remove the backend expression-type side table and the legacy variable inference pass
• require explicit types on every var and static declaration with a focused diagnostic
• support namespaced explicit types such as option::Option
• annotate all affected std::net modules, examples, README snippets, and regression fixtures
• bump the std compatibility revision so older installed compilers cannot parse newer generic struct literals silently

Validation

• cargo fmt --all --check
• cargo test --locked --workspace --jobs 2
• cargo clippy --locked --all-targets --jobs 2 -- -D warnings
• RUSTDOCFLAGS=-D warnings cargo doc --locked --no-deps --jobs 2
• 211/211 Wave corpus files checked
• 20/20 standard-library examples executed
• 114 end-to-end tests passed, 8 environment/architecture skips, 0 failures
• reproduced examples/std/net_tcp.wave successfully with the synchronized installed compiler and std

Closes #407